The present invention relates to a device for improving oil and gas recovery in wells. It can be used in oil and gas industry for oil recovery in oil, condensate and gas fields.
One device of this type is disclosed in U.S. Pat. No. 5,893,414. The device is formed as a tubular element which, by means of a mandrel, is hermetically fixed in a tubing near an interval of perforation and has a system of cavities which are connected with one another. An inlet cone opening is located downwardly and leads to a multi-stage system of coaxially arranged Venturi pipes above the inlet nozzle, with a gradually increasing diameter in direction of flow. From the side of the inlet of the flow into the device, it retains the calculated value of gas in a dissolved condition in oil at a predetermined calculated pressure. On the other hand, the device, accelerates the two-phase flow and creates homogenous structure of gas-liquid flow in upstream direction towards the mouth the opening of the well.
The device has however some disadvantages. The multi-stage structure of the Venturi pipes leads to many small swirling of the flow which can not be accurately calculated on transitions from one diameter of the pipe to the other, so as to make difficult correct forecast of energy losses of the flow, especially in a multi-phase systems, in the device. This in turn makes impossible to forecast an optimal mode of operation of the current condition of the layer and the well, and the process of optimization of the system layer-bottomhole of the well-device-tubing-surface choke. The swirling zones in the device lead to formation of large drops of the liquid (oil-water mixture), which have a speed significantly smaller than the speed of the gas nucleus, and thereby they migrate in direction toward the wall of the tubing so as to create a ring-like mode in the inlet and flowing of the fluid down along the walls of the tubing to a bottomhole of the well. This in turn significantly increases the calculated pressure and therefore reduces efficiency of operation of the well, so as to destabilize its operation and make the process of optimization of the well longer.
Another device is disclosed in U.S. Pat. No. 6,059,040. It includes a Laval nozzle which is hermetically connected with a mandrel and is located inside it, and the mandrel in turn is fixed in a column of pipes. In the narrowest point of the Laval nozzle there are horizontal openings which connect the interior of the Laval nozzle with a space in the tubing above a packer of the mandrel. The device can be used in gas and gas-condensate wells for removal of a liquid phase accumulated in the bottomhole (condensate and water) by creating a zone of low pressure in the narrowest part of the Laval nozzle. The low pressure in this point is created by acceleration of the gas flow. The liquid phase is entrained into the gas flow and broken into small droplets with a structure in form of fog and easily travels to the surface. In the device disclosed in this reference, difficulties take place with the mounting of the device in the mandrel, since for its normal operation it is necessary to drill horizontal openings in the mandrel, which is not possible for the majority of mandrels due to their structural features.